Safety Resource Library

Trenching

Trench Boxes

  • The excavated area between the outside of the trench box and the face of the trench should be as small as possible. The space between the trench box and the excavation side must be backfilled to prevent lateral movement of the box. Shields may not be subjected to loads exceeding those which the system was designed to withstand.
  • Trench boxes are generally used in open areas, but they also may be used in combination with sloping and benching.
  • The box must extend at least 18 inches above the surrounding area if there is sloping toward the excavation. This can be accomplished by providing a benched area adjacent to the box.
  • Any modifications to the shields must be approved by the manufacturer.
  • Shields may ride two feet above the bottom of an excavation, provided they are calculated to support the full depth of the excavation and there is no caving under or behind the shield.
  • Workers must enter and leave the shield in a protected manner, such as by a ladder or ramp.
  • Workers may not remain in the shield while it is being moved.

Ingress and Egress

  • Trenches four feet or more in depth shall be provided with a fixed means of egress.
  • Spacing between ladders or other means of egress must be such that a worker will not have to travel more than 25 feet laterally to the nearest means of egress.
  • Ladders must be secured and extend a minimum of 36 inches above the landing.
  • Metal ladders should not be used when electric utilities are present.

Inspection

Procedures

A competent person shall be placed in charge of all excavations. Underground utilities must be located and marked before excavation begins. Employees are not allowed in the excavation while heavy equipment is digging.

Inspections

The competent person shall conduct inspections:

  • Document the inspection (a checklist works well for this).
  • Daily and before the start of each shift.
  • As dictated by the work being done in the trench.
  • After every rain storm.
  • After other events that could increase hazards, such as a snowstorm, windstorm, thaw, earthquake, dramatic change in weather, etc.
  • When fissures, tension cracks, sloughing, undercutting, water seepage, bulging at the bottom, or other similar conditions occur.
  • When there is a change in the size, location, or placement of the spoil pile.
  • When there is any indication of change or movement in adjacent structures.
  • Written documentation of inspection is recommended.

Protection

  • All excavations or trenches five feet or greater in depth shall be appropriately benched, shored (including trench boxes), or sloped according to the procedures and requirements set forth in OSHA’s Excavation Standard.
  • Excavations or trenches 20 feet deep or greater must have a protective system designed by a registered professional engineer.
  • Excavations under the base of the footing of a foundation or wall require a support system designed by a registered professional engineer.
  • Sidewalks and pavement shall not be undermined unless a support system or another method of protection is provided to protect employees from their possible collapse.

Slope Requirements

SLOPING. Maximum allowable slopes for excavations less than 20 ft. (6.09 m) based on soil type and angle to the horizontal are as follows:

Allowable Slopes

Soil type

Height/Depth ratio

Slope angle

Stable Rock

Verticle

90°

Type A 3/4:1 53°
Type B 1:1 45°
Type C 1 1/2:1 34°
Type A (short-term) 1/2:1 63°
(For a maximum slope angle excavation depth of 12 ft.)

Spoil Pile

  • Temporary spoil shall be placed no closer than 2 feet from the surface edge of the excavation, measured from the nearest base of the spoil to the cut.
  • This distance should not be measured from the crown of the spoil deposit. This distance requirement ensures that loose rock or soil from the temporary spoil will not fall on employees in the trench.
  • Spoil should be placed so that it channels rainwater and other runoff water away from the excavation.
  • Spoil should be placed so that it cannot accidentally run, slide, or fall back into the excavation.

For more complete information visit the OSHA Trenching and Excavation webpage.

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